This invention relates to multi-layered composites of fluorinated polymers and silicon-containing polymers.
Fluoropolymers are a commercially important class of materials that include, for example, crosslinked and uncrosslinked fluorocarbon elastomers and semi-crystalline or glassy fluorocarbon plastics.
Fluorocarbon elastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated and non-halogenated monomers, such as hexafluoropropene, have particular utility in high temperature applications, such as seals, gaskets, and linings. See, for example, R. A. Brullo, xe2x80x9cFluoroelastomer Rubber for Automotive Applications,xe2x80x9d Automotive Elastomer and Design, June 1985, xe2x80x9cFluoroelastomer Seal Up Automotive Future,xe2x80x9d Materials Engineering, October 1988, and W. M. Grootaert, et al., xe2x80x9cFluorocarbon Elastomers,xe2x80x9d Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 8, pp. 990-1005 (4th ed., John Wiley and Sons, 1993).
Fluorocarbon plastics (or fluoroplastics) are generally of high thermal stability and are particularly useful at high temperatures. They also exhibit extreme toughness and flexibility at very low temperatures. Many of these fluoroplastics are almost totally insoluble in a wide variety of solvents and are generally chemically resistant. Some have extremely low dielectric loss and high dielectric strength, and many have unique nonadhesive and low-friction properties. See, for example, F. W. Billmeyer, Textbook of Polymer Science, 3rd ed., pp. 398-403, John Wiley and Sons, New York (1984).
Silicone-containing polymers are also a commercially important class of material. These polymers are known for their wide useful temperature range. See, for example, xe2x80x9cElastomers, Synthetic,xe2x80x9d Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 7, pp. 698-699 (2nd ed., John Wiley and Sons, 1967) and xe2x80x9cSilicones,xe2x80x9d Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 18, pp. 221-260 (2nd ed., John Wiley and Sons, 1969). Silicone-containing polymers, such as silicone-containing elastomers, are also known for their non-stick nature. This feature is a problem when it is desired to use silicone-containing elastomers in combination with other materials.
There are a number of product applications where the advantages of these two polymers are very beneficial. For example many automotive applications require higher performance standards for high and low temperature capabilities, as well as better chemical resistance. One example of these higher performance standards is the new requirements for turbo-charger hose used on some automotive or truck engines. These requirements may be met by the unique combination of properties available from composite structures containing both fluoropolymers and silicone-containing polymers. However, the techniques used to make these composites have not been entirely satisfactory. These techniques include grafting a silicone-containing layer onto an existing cured fluoropolymer substrate (European Pat. No. 0 492 416); grafting unsaturated fluorocarbons onto organosiloxanes (U.S. Pat. No. 4,492,786); and employing a tie layer to adhere a peroxide curable fluoroelastomers to a silicone-containing polymer. These techniques require the use of several processing steps. Often the processes are complicated and time consuming.
There is still a need for an easily manufactured composite of a fluoropolymer directly bonded to a silicone-containing polymer. The bond strength of the resulting composite structures is preferably at least as high as that of the prior art composite structures. More preferably the bond strengths are higher. Additionally the method of making the composite should eliminate the complex and time consuming techniques presently used. Such techniques and materials are preferably useful with bisphenol curable as well as peroxide curable fluoroelastomers and preferable do not require a tie-layer. Single step or in-line processing are particularly desirable.
In accordance with the present invention there is provided a novel composite structure comprising a fluoropolymer adhered directly to a silicone-containing polymer. The composite article comprises
a) a layer of a fluoropolymer selected from the group consisting of fluorothermoplastic polymers and fluoroelastomer polymers, or mixtures thereof, the fluoropolymer having first and second surfaces; and
b) a layer of a cured silicone-containing polymer adhered directly to the first surface of the fluoropolymer.
The two polymers are joined to one another through a transition zone that comprises the reaction product of a peroxide and (i) the fluoropolymer and (ii) the silicone-containing polymer. The peroxide comprises an amount effective to cure the silicone-containing component and to provide the transition zone. The fluoropolymers are selected from melt processable thermoplastic fluoropolymers, fluoroelastomeric fluoropolymers and mixtures thereof.
Also provided is a novel method of bonding a fluoropolymer to a silicone-containing polymer. The method comprises the steps of:
a) providing (i) a fluoropolymer composition comprising a fluoropolymer that is capable of providing a reactive site, and (ii) a curable silicone-containing polymer composition comprising the curable silicone-containing polymer and a peroxide;
b) contacting the fluoropolymer composition with the silicone-containing polymer composition to provide interfacial contact between the two and form a composite structure;
c) exposing the composite structure to conditions sufficient to (i) create the reactive site on the fluoropolymer, (ii) form a transition zone between the fluoropolymer composition and the silicone-containing polymer composition that comprises the reaction product of the peroxide and each of the fluoropolymer composition and the silicone-containing polymer composition, and (iii) bond the fluoropolymer to the silicone-containing polymer.
The composite article demonstrates good bonding between the fluoropolymer and the silicone-containing polymer. These bonds are achieved without the use of a third or tie layer, are preferably at least as good as those achieved with prior art composites. Often they are better. A preferred aspect of the method comprises the addition of a peroxide to both the fluoropolymer composition and the silicone-containing polymer composition.
The method of bonding the fluoropolymer to the silicone-containing polymer eliminates the need for complicated and time consuming processing techniques. It also eliminates the need to use separate tie layers and scrims.
Fluoropolymers
Fluoropolymers used in the invention are capable of providing a reactive site. The reactive site may be provided through dehydrofluorination or by incorporating a reactive comonomer in the polymer. Additionally, the fluoropolymers useful in the invention are capable of interacting with a peroxide to bond to the silicone-containing polymer.
The fluoropolymers may either be vinylidene fluoride containing or substantially non-vinylidene fluoride containing fluoropolymers or mixtures thereof. Additionally, they may be either fluoroplastics (also known as fluorothermoplastics) or fluororubbers (also known as fluoroelastomers) or mixtures thereof. See, for example, American Society for Testing and Materials (ASTM) D 1566 for elastomer and rubber definitions. Preferably, the fluoropolymers are fluoroelastomers. Fluoroplastics are distinguished from fluoroelastomers by their properties. Fluoroplastic materials are melt-processable and have either a melt point and are semi-crystalline, or have a glass transition temperature above ambient temperature. In contrast, fluororubbers are generally amorphous and do not exhibit a melt point. Fluoroplastics and fluororubbers may be used if desired. Additionally, blends of different fluoroplastics or different fluororubbers may be used.
The fluoropolymer used as a starting material in this invention may be provided either in a neat form (i.e., free from other additives) or as a compound (i.e., combined with additives, such as curatives, acid acceptors, fillers, and colorants such as dyes and pigments).
Vinylidene Fluoride Containing Fluoropolymers
These fluoropolymers are derived from vinylidene fluoride (xe2x80x9cVF2xe2x80x9d or xe2x80x9cVDFxe2x80x9d) and fluoropolymers derived from other monomers which, when polymerized, form monomer sequences similar to polymerized vinylidene fluoride. In general, these fluoropolymers will readily dehydrofluorinate when exposed to a base. These other monomers include ethylenically unsaturated monomers which, when incorporated into fluoropolymers, can produce a similar (including an identical) polymeric microstructure as the polymerized VDF. These similarly formed polymers are also prone to dehydrofluorination. In general, the microstructure of a carbon bonded hydrogen atom between carbon bonded fluorine atoms creates a reactive site. The reactivity of a carbon bonded hydrogen is further enhanced when its carbon atom is adjacent to, or attached to a carbon atom possessing a carbon bonded xe2x80x94CF3 group (supplied by HFP or 2-hydropentafluoropropylene for instance) or another electron withdrawing group. Monomers suitable for forming such carbon-bonded-hydrogen reactive sites include, but are not limited to, VDF, 1-hydropentafluoropropene, 2-hydropentafluoropropene, and trifluoroethylene.
The carbon-bonded-hydrogen sites produced upon copolymerization of these monomers, including VDF, can be pre-dehydrofluorinated to form double bonds within the backbone of the fluoropolymer, e.g., before contact with a silicone-containing polymer. This dehydrofluorination reaction may also be produced in situ, e.g., during processing. This in situ dehydrofluorination reaction may be aided by the use of an appropriate catalyst, preferably of the type discussed below. Such VDF-containing fluoropolymers comprise at least 3% by weight of interpolymerized units derived from VDF or other monomers with similar reactivity when polymerized. These VDF-containing fluoropolymers may be homopolymers or copolymers with other ethylenically unsaturated monomers. More preferably, the VDF-containing fluoropolymer is formed from (i) a fluorine-containing monomer selected from the group of vinylidene fluoride, trifluoroethylene, 1-hydropentafluoropropylene, 2-hydropentafluoropropylene, mixtures thereof, and optionally (ii) at least one monomer copolymerizable therewith. In one preferred embodiment, the VDF-containing fluoropolymer comprises a hexafluoropropylene-vinylidene fluoride-tetrafluoroethylene copolymer.
Such VDF-containing fluoropolymers (homopolymers or copolymers) can be made by well-known conventional means, for example by, free-radical polymerization of VDF with or without other ethylenically unsaturated monomers. The preparation of colloidal, aqueous dispersions of such polymers and copolymers is described, for example, in U.S. Pat. No. 4,335,238 (Moore et al.). Customary processes for making such fluoropolymers can include copolymerizing fluorinated olefins in aqueous, colloidal dispersions, which is carried out in the presence of water-soluble initiators which produce free radicals, such as, for example, ammonium or alkali metal persulfates or alkali metal permanganates, and in the presence of emulsifiers, such as, in particular, the ammonium or alkali metal salts of perfluorooctanoic acid.
The VDF-containing fluoropolymers useful in this invention can optionally include other useful fluorine-containing monomers such as hexafluoropropene (HFP), tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), 2-chloropentafluoropropene, a fluorinated vinyl ether, including a perfluoroalkyl vinyl ether such as CF3OCF=CF2 or CF3CF2CF2OCF=CF2. Certain fluorine-containing di-olefins are also useful, such as, perfluorodiallyether and perfluoro-1,3-butadiene.
The VDF-containing fluoropolymers useful in this invention may also comprise interpolymerized units derived from fluorine-free, unsaturated olefin comonomers, e.g., ethylene, propylene or butadiene. Preferably, at least 50% by weight of all monomers in a polymerizable mixture are fluorine-containing. The VDF-containing fluorine-containing monomer may also be copolymerized with iodine- or bromine-containing unsaturated olefin monomer. These monomers, sometimes referred to as cure-site monomers, are useful to prepare a peroxide curable polymer. Suitable cure-site monomers include terminally unsaturated monoolefins of 2 to 4 carbon atoms such as bromodifluoroethylene, bromotrifluoroethylene, iodotrifluoroethylene, and 4-bromo-3,3,4,4-tetrafluoro-1-butene.
Useful commercially available VDF-containing fluoropolymer materials include, for example, THV 200, THV 400, THV 50OG fluoropolymer (available from Dyneon LLC, St. Paul, Minn.), KYNAR(trademark) 740 fluoropolymer (available from Atochem North America, Philadelphia, Pa.), HYLAR(trademark) 700 (available from Ausimont USA, Inc., Morristown, N.J.), and FLUOREL(trademark) FC-2178, FX-9194 and FLS-2650 (available from Dyneon LLC).
Substantially Non-vinylidene Fluoride Containing Fluoropolymers
These fluoropolymers typically do not contain VDF monomer (or any other similar monomer) at a level such that, when polymerized, produces a microstructure which is readily susceptible to reaction with a base, i.e., those that will dehydrofluorinate when exposed to a base, such as an amine. Hence, these fluoropolymers are referred to herein as xe2x80x9csubstantially non-vinylidene fluoride (non-VDF) containing fluoropolymers.xe2x80x9d By xe2x80x9csubstantially non-VDF containing,xe2x80x9d it is meant that the fluoropolymer preferably is substantially free from interpolymerized units derived from VDF monomer, or other monomers which provide a microstructure similar to that described above. These fluoropolymers preferably comprise less than 3%, more preferably less than 1% by weight of interpolymerized units derived from VDF or other monomers which produce a microstructure similar to that described above. However, these must have either hydrogen atoms to allow dehydrofluorination or some other means to provide unsaturation.
Useful substantially non-VDF containing fluoropolymers include melt processable fluoroplastics formed from polymerizing one or more fluorine-containing monomers selected from the group of HFP, TFE, CTFE, and a fluorinated vinyl ether, and may optionally include one or more cure site monomers. Such cure site monomers are typically iodide- or bromide-containing unsaturated olefins. Preferably the cure site monomers are terminally unsaturated monoolefins that contain from 2 to 4 carbon atoms. Examples of useful cure site monomers include bromodifluoroethylene, bromotrifluoroethylene, iodotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1, and mixtures thereof. Particularly useful fluorine-containing monomers are HFP, TFE, and CTFE.
The fluorine-containing monomer used to make the non-VDF containing fluoropolymer may also be copolymerized with fluorine-free unsaturated olefin comonomers, e.g., ethylene, propylene or butadiene. Certain fluorine-containing diolefins are also useful, such as perfluorodiallylether and perfluoro-1,3-butadiene. Preferably at least 50% by weight of all monomers in a polymerizable mixture are fluorine-containing.
Additional examples of fluoroplastics useful in the invention are substantially non-VDF containing copolymers of substantially fluorinated and substantially non-fluorinated olefins. One of these substantially non-VDF containing copolymers is a terpolymer containing TFE, HFP and ethylene. For instance, a useful copolymer contains about 45 mol % to about 75 mol % of TFE units, about 10 mol % to about 30 mol % of HFP units, and about 10 mol % to about 40 mol % of ethylene units and has a melting point of about 140xc2x0 C. to about 250xc2x0 C.
Another example of a useful fluoroplastic in the present invention comprises interpolymerized units derived from TFE and allylic hydrogen-containing olefin monomer. International Publication No. WO 96/18665 (Greuel) describes fluoropolymers and preferred methods of producing interpolymerized units derived from TFE and polypropylene. The copolymers can generally contain, e.g., from about 2 weight percent to about 20 weight percent (preferably from about 5 weight percent to about 15 weight percent, more preferably from about 7 weight percent to about 12 weight percent) allylic hydrogen-containing olefin monomer. These semi-crystalline copolymers typically have melt temperatures so that they can be processed at temperatures below about 300xc2x0 C., preferably from about 200xc2x0 C. to about 250xc2x0 C.
Examples of useful substantially non-VDF containing fluoropolymers of this type include poly(ethylene-co-tetrafluoroethylene), poly(tetrafluoroethylene-co-propylene), poly(chlorotrifluoroethylene-co-ethylene), and the terpolymer poly(ethylene-co-tetrafluoroethylene-co-hexafluoropropylene), as well as perfluorinated melt processable plastics, among others. Also, many useful substantially non-VDF containing fluoropolymer materials are commercially available,, for example from Dyneon, LLC, St. Paul, Minn., under the trade designations X6810, and X6820; from Daikin America, Inc., Decatur, Ala., under the trade designations NEOFLON EP-541, EP-521, and EP-610; from Asahi Glass Co., Tokyo, Japan, under the trade designations AFLON COP C55A, C55AX, C88A; from DuPont, Wilmington, Del., under the trade designations TEFZEL 230 and 290; AFLAS series of copolymers from Asahi Glass Co., and VITON ETP 500 and 900 from DuPont Dow Elastomers.
Many ways to make such polymers (including copolymers, terpolymers, etc.) are known. Such methods include, but are not limited to, suspension free-radical polymerization or conventional emulsion polymerization, which typically involve polymerizing monomers in an aqueous medium in the presence of an inorganic free-radical initiator system and surfactant or suspending agent. In general, the desired olefinic monomers can be copolymerized in an aqueous colloidal dispersion in the presence of water-soluble initiators which produce free radicals such as, for example, ammonium or alkali metal persulfates or alkali metal permanganates, and in the presence of emulsifiers such as, in particular, ammonium or alkali metal salts of perfluorooctanoic acid. See, for example, U.S. Pat. No. 4,335,238.
The substantially non-VDF containing fluoropolymers are comprised of essentially fluorinated and essentially non-fluorinated olefins. They can be prepared using a fluorinated sulfinate as a reducing agent and a water soluble oxidizing agent capable of converting the sulfinate to a sulfonyl radical. Preferred oxidizing agents are sodium, potassium, and ammonium persulfates, perphosphates, perborates, and percarbonates. Particularly preferred oxidizing agents are sodium, potassium, and ammonium persulfates.
Aqueous emulsion and suspension polymerizations can be carried out in conventional steady-state conditions in which, for example, monomers, water, surfactants, buffers and catalysts are fed continuously to a stirred reactor under optimum pressure and temperature conditions while the resulting emulsion or suspension is removed continuously. An alternative technique is batch or semibatch polymerization by feeding the ingredients into a stirred reactor and allowing them to react at a set temperature for a specified length of time or by charging ingredients into the reactor and feeding the monomer into the reactor to maintain a constant pressure until a desired amount of polymer is formed.
Because the substantially non-VDF containing fluoropolymers are not readily susceptable to dehydrofluorination, it is necessary that either relatively aggressive dehydrofluorinating techniques be employed or that a reactive comonomer be employed in the fluoropolymer.
Fluoroelastomers
Fluoroelastomers used in the present invention are preferably polymers of one or more fluoromonomers selected from the group of vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, 2-chloropentafluoropropylene, perfluorinated alkyl vinyl ether, perfluorinated alkyl allyl ether, tetrafluoroethylene, 1-hydropentafluoropropylene, dichlorodifluoroethylene, trifluoroethylene, 1,1-chlorofluoroethylene, 1,2-difluoroethylene, bromotrifluoroethylene, bromodifluoroethylene, and bromotetrafluorobutene. Optionally, the aforementioned one or more fluoromonomers may be copolymerized with fluorine-free olefinic monomers such as ethylene and propylene.
The preferred fluoroelastomers are copolyiners of vinylidene fluoride, hexafluoropropylene, and optionally tetrafluoroethylene. Preferably these polymers comprise between about 15 and about 50 mole percent hexafluoropropylene, and up to 30 mole percent tetrafluoroethylene. Mixtures or blends of different fluorinated elastomers, and fluoroelastomers of different viscosities or molecular weights, are also suitable.
There are a number of commercially available fluoroelastomers that can be used in the invention. These include the FLUOREL(trademark) fluoroelastomers sold by Dyneon LLC of St. Paul, Minn. Examples of these fluoroelastomers include, FE, FC, FT, FG, FLS and FX grades. Other commercially available fluoroelastomers that may be used in the invention include the TECNOFLON(trademark) fluoroelastomers (available from Ausimont S.p.A. of Milan, Italy), the VITON(trademark) fluoroelastomers (available from DuPont-Dow LLC of Wilmington, Del.) and the DAIEL(trademark) fluoroelastomers (available from Daikin Industries Ltd.).
Fluoroplastics
Fluoroplastics containing similar monomers as discussed above are also useful in this invention. The same preference exists for vinylidene fluoride containing polymers and copolymers. If the fluoroplastic is a substantially non-VDF containing polymer than more aggresive dehydrofluorinating agents or bases should be employed as discussed above.
Additionally, useful fluoroplastics are preferably processed at a temperature that is compatible with the processing temperature of the silicone-containing component selected. Silicone materials are generally processed at lower temperatures than many fluoroplastics and thus the cure systems for silicone-containing materials are generally activated at lower temperatures. The cure of the silicone-containing component should not be substantially completed before the chemical activity associated with the bonding of the component layers has been substantially completed.
There are several options for selecting a suitable fluoroplastic. For example, one can select a fluoroplastic having a low temperature processing temperature such as THV 200, available from Dyneon LLC in St. Paul, Minn. Alternatively, one can select a silicone curative system which activates at a higher temperature, e.g. Trigonox(trademark) 145-45B, relative to curatives normally used for silicone elastomers. Combinations of these two approaches may also be used depending on the process restrictions present or the properties desired in the final composite.
Yet another option is to use a blend of a fluoroelastomer and a fluoroplastic material. Where processing temperature is a concern, the blend may comprise a major portion of fluoroelastomer and a minor portion of fluoroplastic. Where performance advantages for permeation, for example, are of primary concern, the major portion may be fluoroplastic and the minor portion fluoroelastomer, with appropriate attention to selection of silicone curative and fluoroplastic as discussed herein.
Useful commercially available fluoroplastics include, for example, the THV 200 and 300 and the HTE 1500 and 1700 fluoropolymers available from Dyneon.
Dehydrofluorinating Agent
The fluoropolymer used in the composite article may be dehydrofluorinated in order to provide the reactive site. There are a number of materials that can be used to effect dehydrofluorination. These materials include the organo-onium compounds used to cure fluoroelastomers.
Examples of materials useful as dehydrofluorinating agents include organo-oniums, such as those discussed in the section below entitled xe2x80x9cAccelerator.xe2x80x9d Another class of useful dehydrofluorinating agents are strong bases, such as 1,8 diaza[5.4.0]bicyclo undec-7-ene, (DBU) and 1,5-diazabicyclo[4.3.0]-5-nonene, (DBN). Preferred dehydrofluorinating agents include tributyl(2-methoxy)-propylphosponium chloride, triphenyl benzyl phosphonium chloride, complexes of tributyl(2-methoxy)-phosphonium chloride with bisphenol AF, and DBU. Combinations of dehydrofluorinating agents may be employed if desired.
If the fluoropolyiner lacks reactives sites, an effective amount of the dehydrofluorinating agent must be employed. An effective amount is that quantity of dehydrofluorinating agent necessary to bond the fluoropolymer to the silicone-containing polymer. The exact quantity of dehydrofluorinating agent employed is dependent upon the fluoropolymer employed and the reactivity of the other additives used.
Within these parameters, an effective amount of dehydrofluorinating agent is generally from 0.01 to 20 parts per one hundred parts of the fluoropolymer. Preferred addition levels are from 0.1 to 5 parts per hundred. A measure of effectiveness is a bond strength of at least 0.4 kg/cm. A preferred bond strength is at least 1 kg/cm and more preferred is an increase of 2 kg/cm or greater.
Cure Site Monomers
The fluoropolymer may employ reactive site derived from a reactive comonomer. Such comonomers (also known as cure-site monomers) include, for example, copolymerizable bromine-containing or iodine-containing terminally unsaturated olefins of two to four carbon atoms in which at least one hydrogen atom is substituted by bromine or iodine and optionally one or more of the remaining hydrogen atoms have been replaced by fluorine. Such olefins include 4-bromo-perfluorobutene-1, vinyl bromide, pentafluoroallyl bromide, 4-bromo-difluorobutene-1,2-bromoheptafluorobutene-1,3-bromoheptafluorobutene-1, difluoroallyl bromide, bromotrifluoroethylene and 1-bromo-2,2-difluoroethylene, iodotrifluoroethylene, 3-bromo-4-iodoperfluorobutene-1 and 2-bromo-4-iodoperfluorobutene-1. Preferably the cure-site monomer is reactive with a peroxide.
Silicone-Containing Polymer
Silicone-containing polymers used in the invention are elastomeric. They generally comprise linear polydimethylsiloxane and are of sufficiently high molecular weight to provide the desired properties. The molecular weight is generally greater than about 5xc3x97105. The silicone polymers preferred in this invention are vinyl-containing silicone elastomers. Such silicone elastomers are generally cured or vulcanized at temperature above room temperature. Many silicone elastomers are supplied preblended with the catalysts or curatives required.
Methods of Compounding
In accordance with this invention, the desired amount of components for each composition are added together and intimately admixed. It is preferred that the temperature of the polymer compositions not rise to a level sufficient to cause curing. During mixing it is highly desirable to distribute the components and adjuvants uniformly throughout the polymer compositions.
Method of Forming Composite Articles
In the present invention, the fluoropolymer and silicone-containing polymer are preferably intimately bonded to one another. As used herein, the term xe2x80x9cintimately bondedxe2x80x9d means that the components or layers are not easily physically separated without substantially destroying the composite or multi-layer article. Additionally, any of the embodiments contemplated by the invention can be provided in a form of a sheet or film or multilayered tubing or hose or other shaped article regardless of the specific embodiments discussed in the examples. Further, the order of the layers may be reversed in any of these embodiments. Determination of what comprises the inner and outer layers may be influenced by where the barrier properties and/or chemical or temperature resistant properties are desired.
Methods known in the polymer art can be used to produce a composite article, such as a bonded multi-layer article, wherein the fluoropolymer component is in substantial contact with the silicone-containing polymer. For instance, the polymer components can be formed into thin films or thicker sheets by known methods. These films or sheets can be laminated together under heat and pressure to form a bonded multi-layer article. Alternatively, the components can be simultaneously co-extruded or co-injection molded into a multi-layer article, including films or tubing.
Conditions by which two or more components are brought together (e.g., sequential extrusion, co-extrusion, co-injection molding or lamination, to name a few) may be sufficient to provide adequate adhesion between the components. However, it may be desirable to further treat the resulting composite article with, for example, heat and pressure to improve adhesion. In the case where one or more of the components require a cure step, such as for the fluoropolymer, heat and, possibly pressure will be required. One way to supply such heat and pressure is to pass the composite through an autoclave. A steam autoclave, for example, may supply both heat and pressure. In the case of multilayered hoses, the curing step may take place after the hose is formed, and may also take place on a mandrel which shapes the part even further prior to the final cure;
To provide additional heat only, for example, one may slow the rate of cooling after extrusion or forming of the components. Also, additional heat or energy can be added during or after extrusion or lamination processes, wherein the temperatures may be higher than that required for merely processing the components. Further, the complete composite article may be held at an elevated temperature and/or pressure for an extended period of time, such as in an oven, an autoclave, a heated liquid bath and the like. A combination of these methods can also be used.
Formation of the composite article of the invention is achieved, for example, by (a) providing a fluoropolymer composition and a silicone-containing polymer composition, (b) contacting the two compositions to one another at an interface, and exposing the two compositions to provide the transition zone.
The fluoropolymer composition comprises the fluoropolymer, and optionally, the dehydrofluorinating agent, a curative, an accelerator, a coagent, and metal oxide. When a dehydrofluorinating agent is used, it should be used in combination with an acid acceptor. Other optional additives include process aids, pigments, and the like.
Curative For Fluoropolymers
A curative (or crosslinking agent) is typically used when the fluoropolymer contains a reactive site derived from a cure site monomer or when the reactive site is due to dehydrofluorination of the fluoropolymer. Useful curatives for VDF containing fluoropolymers include both the conventional curing agents used to cure fluoroelastomers, i.e., organic and inorganic peroxides, polyhydroxy compounds or derivatives thereof, organic polyamines or derivatives thereof, and fluoroaliphatic polyols and allyl ethers and carbonates of aromatic polyhydroxy compounds.
The polyhydroxy compounds and their derivatives represent a preferred class of curatives. The compounds are well known and are described in the art in U.S. Pat. Nos. 4,259,463; 3,876,654; 4,233,421 and 5,262,490. Polyhydroxy compounds useful in the invention are also described in U.S. Pat. Nos. 3,655,727; 3,721,877; 3,857,807; 3,686,143; 3,933,372; and 4,358,559. The disclosures of these references with regard to these compounds is incorporated herein by reference. These compounds can be either aromatic or aliphatic polyhydroxy compounds or their derivatives. Blends of such compounds may be used if desired.
Representative examples of useful crosslinking agents are:
Hydroquinone, resorcinol
4,4xe2x80x2-dihydroxydiphenylsulfone (Bisphenol S)
2,4xe2x80x2-dihydroxydiphenylsulforie
2,2-isopropylidine-bis(4-hydroxybenzene) (Bisphenol A)
2,2-hexafluoroisopropylidine-bis(4-hydroxybenzene) (Bisphenol AF)
4,4xe2x80x2-dihydroxybenzophenone
4,4xe2x80x2-biphenol
1-allyloxy-4-hydroxybenzene
Bisphenol A monoallyl ether
Dicarbonate blocked Bisphenol AF compounds
1,4-bis(hydroxymethyl)perfluorobutane
Hexamethylenediaminne carbamate
N,Nxe2x80x2-dicinnamylidene-1,6-hexanediamine.
Mixtures of the foregoing can also be used.
The Accelerator
When using polyhydroxy compounds as curing agents, an accelerator is also normally used. A class of accelerators useful in the invention are the organo-onium compounds.
The organo-onium compounds are phosphonium, ammonium, or sulfonium compounds which are conjugate acids of a phosphine, amine, or sulfide. They can be formed by reacting said phosphine, amine, or sulfide with a suitable alkylating agent (e.g., an alkyl halide or aryl halide) resulting in the expansion of the valence of the electron donating phosphorous, nitrogen, or sulfur atom and a positive charge on the organo-onium compound. The organo-onium compounds suitable for use in this invention are known and are described in the art. See, for example, U.S. Pat. No. 4,882,390 (Grootaert et al.), U.S. Pat. No. 4,233,421 (Worm), U.S. Pat. No. 5,086,123 (Guenthner et al.), and U.S. Pat. No. 5,262,490 (Kolb et al.) which descriptions are incorporated by reference.
Said phosphonium compounds include those selected from the group consisting of amino-phosphonium, phosphorane (e.g., triarylphosphorane), and phosphorous containing iminium compounds.
One class of phosphonium or ammonium compounds broadly comprises relatively positive and relatively negative ions (the phosphorous or nitrogen atom generally comprising the central atom of the positive ion), these compounds being generally known as ammonium or phosphonium salts or compounds.
Another class of phosphonium compounds useful in this invention are amino-phosphonium compounds some of which are described in the art, see for example, U.S. Pat. No. 4,259,463 (Moogi et al.).
Another class of phosphonium compounds useful in this invention are phosphorane compounds such as triarylphosphorane compounds; some of the latter compounds are known and are described in the art, see for example, U.S. Pat. No. 3,752,787 (de Brunner), which descriptions are herein incorporated by reference.
Another class of iminium compounds useful in this invention are described in the art, e.g., European Patent Applications 182299A2 and 120462A1 which descriptions are herein incorporated by reference. Examples of such iminium compounds include bis(benzyldiphenyl phosphine)iminium chloride and bis(triphenyl phosphine)iminium nitrate.
Representative phosphoniuim compounds include tetramethylphosphonium chloride, tetrabutylphosphonium chloride, tributylbenzyl phosphonium chloride, tributylallylphosphonium chloride, tetraphenylphosphonium chloride, benzyltris(dimethylamino)phosphonium chloride, bis(benzyldiphenylphosphine)iminium chloride, and triphenylbenzylphosphonium chloride.
Sulfonium compounds useful in this invention are known and described in the art, e.g., see U.S. Pat. No. 4,233,421 (Worm). Briefly described, a sulfonium compound is a sulfur-containing organic compound in which at least one sulfur atom is covalently bonded to three organic moieties having from 1 to 20 carbon atoms by means of carbon-sulfur covalent bonds and is ionically associated with an anion. Said organic moieties can be the same or different. The sulfonium compounds may have more than one relatively positive sulfur atom, e.g., [(C6H5)2S+C6H4S+(C6H5)2]2Clxe2x88x92, and two of the carbon-sulfur covalent bonds may be between the carbon atoms of a divalent organic moiety, i.e., the sulfur atom may be a heteroatom in a cyclic structure.
Co-Agent
A multifunctional coagent is another optional, but beneficial additive. The benefits of using such multifunctional coagents include increasing the bond strength, as well as the cross link density of the fluoropolymer as evidenced by higher mechanical strength. Useful coagents include such multifunctional materials as triallylisocyanurate (TAIC), 1,2-vinyl polybutadiene, triallyl cyanurate, triallyl trimellitate, N,Nxe2x80x2-m-phenylenebismaleimide, diallyl phthalate and triallyl phosphite. Combinations of such coagents are also useful and may be preferred. Useful addition levels include from 0.01 to 20 parts per one hundred parts of the fluoropolymer (or total fluoropolymer in the case of a blend of fluoropolymers). Preferred addition levels are from 1 to 5 parts per hundred.
Metal Oxide
Yet another optional, but beneficial additive is a metal oxide. The preferred metal oxides is calcium oxide. Typically the metal oxide is used at a level of from 1 to 35 parts per 100 parts by weight of the neat fluoropolymer.
Peroxide
Peroxides may also be used with the fluoropolymer composition. This includes fluoropolymers which are polyhydroxy-curable, e.g., bisphenol, and diamine-curable, as well as those fluoropolymers which are normally cured by the addition of peroxide. The peroxide added to the fluoropolymer should not be slower reacting than the peroxide used in the silicone-containing composition. Preferably, the peroxide added to the fluoropolymer composition will be substantially equal in reactivity to the peroxide added to the silicone-containing composition. It is desirable that the chemical or bonding activity at the interface between the fluoropolyiner and the silicone-containing component does not substantially lag behind the cure reaction of the silicone-containing component.
Useful addition levels include from 0.1 to 10 parts per one hundred parts of the fluoropolymer (or total fluoropolymer in the case of a blend of fluoropolymers). Preferred addition levels are from 0.5 to 5 parts per hundred parts of fluoropolymer.
Other Optional Additives
A variety of other adjuvants may be employed in the fluoropolymer compositions. Such materials include colorants (such as dyes and pigments), processing aids, and reinforcing fillers. Optional additives may be employed provided they do not significantly affect the bond between the fluoropolymer and the silicone-containing polymer.
Silicone-Containing Component
The silicone-containing polymer composition comprises the silicone-containing polymer, a curative for the silicone-containing polymer and optional additives for the silicone-containing polymer.
Curative For Silicone-Containing Component
Curatives for the silicone elastomers include peroxides. Such peroxides generally provide the cross-linking feature of the cure or vulcanization process through a free radical generation process.
Useful peroxides for this invention are selected based on the rate of cure in the silicone elastomer. Silicone-containing elastomers are generally cured at temperature above room temperature, but at temperatures lower than those used for curing fluorinated elastomers. Such lower cure temperatures normally require curing agents, e.g., peroxides, with a low activation energy, i.e., only a low temperature is required to activate the curative.
In this invention, however, it is preferred that the activation energy of the peroxide curative selected for use in the silicone elastomer should be no less than the activation energy of the peroxide added to the fluoropolymer component. It is more preferred that the activation energy of each peroxide selected be substantially equal. The curing temperature listed for the peroxide curatives in the Examples is related to the activation energy of the curative. Generally speaking, the lower the curing temperature listed, the lower the activation energy of the curative. If the reactive site of the fluoropolymer is provided by dehydrofluorination, the peroxide to be added to the silicone component should be selected such that the silicone-containing polymer does not substantially cure before the reactive sites in the fluoropolymer, that allow the bonding, have been formed.
Useful peroxides include di-t-butyl peroxide, benzoyl peroxide, di(p-cumyl) peroxide and di(p-chlorophenyl) peroxide available commercially under Tradenames such as Perkadox and Luperco.
Useful addition levels include from 0.1 to 10 parts per one hundred parts of the silicone-containing compound, i.e., including the weight of other additives in the silicone-containing component, not just the weight of the gum. Preferred addition levels are from 0.5 to 3 parts per hundred. These amounts are in addition to any peroxides added to the fluoropolymer component.
Additives for Silicone Elastomers
Additives, such as, for example, extending fillers, process aids, antioxidants and pigments are commonly used to obtain certain performance characteristics. Fumed silica is a common filler used to reinforce strength properties. Other additives used include precipitated silica, titanium dioxide, calcium carbonate, magnesium oxide and ferric oxide.
Such additives may be available pre-mixed into the silicone elastomer gum. A 2-roll mill is a common method of addition of these reactive elements because such a mill has the ability to control temperature, or more importantly, to remove heat generated during the mixing process.
The many advantages of a composite article in accordance with the invention are further illustrated by the following non-limiting examples in which all parts are given as parts by weight unless otherwise stated. Parts in the fluoropolymer compositions are based upon parts per one hundred parts of the polymer to which the ingredients are added (pphr) unless stated otherwise. Parts in the silicone-containing component are based upon parts per one hundred parts of the total silicone-containing compound, including all additives, unless stated otherwise.